Various laser procedures or operations require that a laser beam be properly focused to a specific focal point. For example, in ophthalmic laser surgery wherein eye tissue is to be photodisrupted or ablated in or on the tissue that is to be affected, the correct positioning of a focusing assembly used to focus a laser beam is very critical. Such ophthalmic surgical procedures include those in cornea, sclera, iris, the crystalline lens and related structures, vitreous, and retina, and for treatment of glaucoma. Focal depth precision is also required in many non-ophthalmic laser surgical procedures, such as applications in dermatology and even “surgery” in DNA to excise portions of chromosomes. Also, non-biologic applications, such as photolithography and micromachining require focal depth precision.
With presently used laser systems, however, it is a critical concern that the object be positioned in a known relationship relative to the laser system. For example, in eye surgery, it is only when the eye can be positioned in a known relationship relative to the laser system that the laser beam can be directed to the desired area inside the eye with a high degree of accuracy. This is important because an inaccurately or improperly directed laser beam could affect an area of the eye not desired to be treated and cause permanent damage to the eye.
One way to accurately position the eye relative to a laser system for the purposes of performing laser ophthalmic procedures is to use a contact lens to stabilize the eye. To do this, however, the alignment of the contact lens (glass plate or “aplanation lens”) relative to the laser system must be known. As indicated above, if the lens alignment relative to the laser beam is not known, errors in accurate positioning of the laser beam can result.
In order to ensure that the alignment of a contact lens is known relative to a laser system, it is possible to permanently mount the lens on the laser system in a fixed orientation. If the contact lens is to remain mounted on the laser system, however, sterilization of the lens after each laser ophthalmic procedure could be time consuming, difficult to accomplish and, most likely, very uneconomical. Alternatively, the contact lens could be removed from the laser system, sterilized, and replaced. Further, a disposable contact lens could be used for the laser ophthalmic procedure. For either of these last two alternatives, however, the contact lens will require realignment with the laser system after the lens is mounted on the laser system.
U.S. Pat. No. 6,373,571 (incorporated herein by reference for all purposes) issued to Juhasz et al., discloses a system and method for aligning an aplanation lens with a laser system. In particular, Juhasz discloses that in order to properly align the aplanation lens to a laser system, reference marks on the contact lens are brought into coincidence with predetermined focal points along the laser beam paths. To this end, the laser system successively directs a laser beam along at least three predetermined paths to respective predetermined focal points, and the contact lens is positioned across these predetermined paths. Along each predetermined path, the laser beam is activated to establish a series of laser marks on the contact lens. If the laser marks, predetermined focal points, and reference marks are all coincident, then the contact lens is properly aligned with the laser system. If there is any displacement between any laser mark and reference mark, however, a retainer ring holding the aplanation lens is adjusted to align all reference marks with all predetermined focal points to align the lens to the laser system.
Because of the foregoing, it is however desirable to have alternative system and methods to determine the position and alignment of a plane of an object in relation to an intersecting axis and using that known position and alignment to allow for corrections to be made when using the plane as a reference plane.